U.S. patent application number 14/302317 was filed with the patent office on 2015-12-17 for methods and apparatuses for hydrocracking heavy and light hydrocarbons.
The applicant listed for this patent is UOP LLC. Invention is credited to Scott M. Roney.
Application Number | 20150361358 14/302317 |
Document ID | / |
Family ID | 54835633 |
Filed Date | 2015-12-17 |
United States Patent
Application |
20150361358 |
Kind Code |
A1 |
Roney; Scott M. |
December 17, 2015 |
METHODS AND APPARATUSES FOR HYDROCRACKING HEAVY AND LIGHT
HYDROCARBONS
Abstract
Methods and apparatuses for processing hydrocarbons are
provided. In one embodiment, a method for processing a hydrocarbon
stream including lighter hydrocarbons and heavier hydrocarbons
includes hydrocracking the lighter hydrocarbons in a hydrocracking
reactor. After hydrocracking the lighter hydrocarbons, the method
hydrocracks the heavier hydrocarbons in the hydrocracking reactor.
The method includes removing from the hydrocracking reactor a
hydrocracking effluent comprising a mixture of components formed by
hydrocracking the lighter hydrocarbons and hydrocracking the
heavier hydrocarbons.
Inventors: |
Roney; Scott M.; (Wheaton,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UOP LLC |
Del Plaines |
IL |
US |
|
|
Family ID: |
54835633 |
Appl. No.: |
14/302317 |
Filed: |
June 11, 2014 |
Current U.S.
Class: |
208/78 ;
422/187 |
Current CPC
Class: |
C10G 2400/04 20130101;
C10G 65/12 20130101; C10G 2400/02 20130101; C10G 2400/06 20130101;
C10G 65/18 20130101; C10G 65/10 20130101; C10G 2400/08
20130101 |
International
Class: |
C10G 65/18 20060101
C10G065/18 |
Claims
1. A method for processing a hydrocarbon stream including lighter
hydrocarbons and heavier hydrocarbons, the method comprising:
hydrocracking the lighter hydrocarbons in a hydrocracking reactor;
after hydrocracking the lighter hydrocarbons, hydrocracking the
heavier hydrocarbons in the hydrocracking reactor; and removing
from the hydrocracking reactor a hydrocracking effluent comprising
a mixture of components formed by hydrocracking the lighter
hydrocarbons and hydrocracking the heavier hydrocarbons.
2. The method of claim 1 wherein: hydrocracking the lighter
hydrocarbons in the hydrocracking reactor comprises hydrocracking
hydrocarbons having boiling points below about 480.degree. C.
(about 900.degree. F.); and hydrocracking the heavier hydrocarbons
in the hydrocracking reactor comprises hydrocracking hydrocarbons
having boiling points above about 425.degree. C. (about 800.degree.
F.).
3. The method of claim 1 wherein hydrocracking the lighter
hydrocarbons comprises hydrocracking over 50 wt % of the lighter
hydrocarbons, based on the total weight of the lighter
hydrocarbons, before hydrocracking the heavier hydrocarbons.
4. The method of claim 1 wherein hydrocracking the lighter
hydrocarbons comprises hydrocracking over 60 wt % of the lighter
hydrocarbons, based on the total weight of the lighter
hydrocarbons, before hydrocracking the heavier hydrocarbons.
5. The method of claim 1 wherein hydrocracking the lighter
hydrocarbons comprises hydrocracking over 70 wt % of the lighter
hydrocarbons, based on the total weight of the lighter
hydrocarbons, before hydrocracking the heavier hydrocarbons.
6. The method of claim 1 wherein removing from the hydrocracking
reactor the hydrocracking effluent comprises removing the
hydrocracking effluent comprising at least about 80 wt % of
hydrocarbons having boiling points of less than about 382.degree.
C. (720.degree. F.), based on the total weight of hydrocarbons
having boiling points of less than about 382.degree. C.
(720.degree. F.).
7. The method of claim 1 wherein the hydrocarbon stream further
includes heaviest hydrocarbons having a higher boiling temperature
than the heavier hydrocarbons, and wherein the method further
comprises: after hydrocracking the heavier hydrocarbons,
hydrocracking the heaviest hydrocarbons in the hydrocracking
reactor, wherein removing from the hydrocracking reactor a
hydrocracking effluent comprises removing from the hydrocracking
reactor a hydrocracking effluent formed by hydrocracking the
lighter hydrocarbons, hydrocracking the heavier hydrocarbons, and
hydrocracking the heaviest hydrocarbons.
8. A method for processing hydrocarbons, the method comprising the
steps of: fractionating the hydrocarbons into a stream rich in
lighter hydrocarbons and a stream rich in heavier hydrocarbons;
feeding the stream rich in lighter hydrocarbons to an upstream
location in a hydrocracking zone; hydrocracking the stream rich in
lighter hydrocarbons to form lighter hydrocracking products;
feeding the stream rich in heavier hydrocarbons into the lighter
hydrocracking products at a downstream location in the
hydrocracking zone; and hydrocracking the stream rich in heavier
hydrocarbons to form heavier hydrocracking products.
9. The method of claim 8 wherein fractionating the hydrocarbons
comprises fractionating the hydrocarbons into the stream rich in
lighter hydrocarbons having an initial boiling point of about
370.degree. C. (about 700.degree. F.) and into the stream rich in
heavier hydrocarbons having a final boiling point of from about
510.degree. C. to about 590.degree. C. (about 950.degree. F. to
about 1100.degree. F.).
10. The method of claim 8 further comprising feeding hydrogen to
the upstream location in the hydrocracking zone, wherein the stream
rich in heavier hydrocarbons quenches the lighter hydrocracking
products at the downstream location in the hydrocracking zone.
11. The method of claim 8 wherein: feeding the stream rich in
lighter hydrocarbons to an upstream location in a hydrocracking
zone comprises feeding the stream rich in lighter hydrocarbons to
an upper bed in a hydrocracking reactor; and feeding the stream
rich in heavier hydrocarbons into the lighter hydrocracking
products at the downstream location in the hydrocracking zone
comprises feeding the stream rich in heavier hydrocarbons to a
lower bed in the hydrocracking reactor, wherein the fraction of the
total catalyst volume in the upper bed does not exceed the volume
fraction of the total hydrocarbons fed to the upper bed.
12. The method of claim 8 wherein fractionating the hydrocarbons
comprises fractionating the hydrocarbons into the stream rich in
lighter hydrocarbons, the stream rich in heavier hydrocarbons, and
a stream rich in heaviest hydrocarbons, the method further
comprising: feeding the stream rich in heaviest hydrocarbons into
the lighter hydrocracking products and the heavier hydrocracking
products at a farther downstream location in the hydrocracking
zone; and hydrocracking the stream rich in heaviest hydrocarbons to
form heaviest hydrocracking products.
13. The method of claim 12 wherein fractionating the hydrocarbons
comprises fractionating the hydrocarbons into the stream rich in
lighter hydrocarbons having boiling points of less than about
425.degree. C. (less than about 800.degree. F.), into the stream
rich in heavier hydrocarbons having boiling points of from about
425.degree. C. to about 480.degree. C. (about 800.degree. F. to
about 900.degree. F.), and into the stream rich in heaviest
hydrocarbons having boiling points of greater than about
480.degree. C. (900.degree. F.).
14. The method of claim 12 wherein: feeding the stream rich in
lighter hydrocarbons to an upstream location in a hydrocracking
zone comprises feeding the stream rich in lighter hydrocarbons to a
first bed in a hydrocracking reactor; feeding the stream rich in
heavier hydrocarbons into the lighter hydrocracking products at the
downstream location in the hydrocracking zone comprises feeding the
stream rich in heavier hydrocarbons to a second bed below the first
bed in the hydrocracking reactor; and feeding the stream rich in
heaviest hydrocarbons into the lighter hydrocracking products and
the heavier hydrocracking products at the farther downstream
location in the hydrocracking zone comprises feeding the stream
rich in heaviest hydrocarbons to a third bed below the second bed
in the hydrocracking reactor; and wherein: the fraction of the
total catalyst volume in the first bed does not exceed the volume
fraction of the total hydrocarbons fed to the first bed; and the
fraction of the total catalyst volume in the second bed does not
exceed the volume fraction of the heavier hydrocarbons fed to the
second bed.
15. The method of claim 8 wherein hydrocracking the stream rich in
lighter hydrocarbons to form lighter hydrocracking products
comprises hydrocracking over 50 wt % of the stream rich in lighter
hydrocarbons before feeding the stream rich in heavier hydrocarbons
into the lighter hydrocracking products.
16. The method of claim 8 wherein hydrocracking the stream rich in
lighter hydrocarbons to form lighter hydrocracking products
comprises hydrocracking over 60 wt % of the stream rich in lighter
hydrocarbons before feeding the stream rich in heavier hydrocarbons
into the lighter hydrocracking products.
17. The method of claim 8 wherein hydrocracking the stream rich in
lighter hydrocarbons to form lighter hydrocracking products
comprises hydrocracking over 70 wt % of the stream rich in lighter
hydrocarbons before feeding the stream rich in heavier hydrocarbons
into the lighter hydrocracking products.
18. The method of claim 8 further comprising recovering the lighter
hydrocracking products and the heavier hydrocracking products as a
hydrocracking effluent.
19. The method of claim 18 wherein recovering the lighter
hydrocracking products and the heavier hydrocracking products as
the hydrocracking effluent comprises recovering the hydrocracking
effluent comprising at least about 80 wt % of hydrocarbons having
boiling points of less than about 382.degree. C. (720.degree.
F.).
20. An apparatus for processing a hydrocarbon stream, the apparatus
comprising: a fractionation unit having an upper outlet and a lower
outlet and configured to discharge a stream rich in lighter
hydrocarbons from the upper outlet and a stream rich in heavier
hydrocarbons from the lower outlet; a hydrocracking reactor having
an upper inlet in fluid communication with the upper outlet of the
fractionation unit for receiving the stream rich in lighter
hydrocarbons, an upper hydrocracking zone for hydrocracking the
stream rich in lighter hydrocarbons, a lower inlet in fluid
communication with the lower outlet of the fractionation unit for
receiving the stream rich in heavier hydrocarbons, and a lower
hydrocracking zone for hydrocracking the stream rich in heavier
hydrocarbons.
Description
TECHNICAL FIELD
[0001] The technical field generally relates to methods and
apparatuses for processing hydrocarbons, and more particularly
relates to methods and apparatuses for efficiently hydrocracking
both heavy and light hydrocarbons.
BACKGROUND
[0002] Petroleum refiners often produce desirable products, such as
turbine fuel, diesel fuel and other products known as middle
distillates, as well as lower boiling hydrocarbonaceous liquids,
such as naphtha and gasoline, by hydrocracking a hydrocarbon
feedstock derived from crude oil or heavy fractions thereof.
Feedstocks most often subjected to hydrocracking are the gas oils
and heavy gas oils recovered from crude oil by distillation. A
typical heavy gas oil comprises a substantial portion of
hydrocarbon components boiling above 370.degree. C. (700.degree.
F.). A typical vacuum gas oil has a boiling point range between
315.degree. C. (600.degree. F.) and about 565.degree. C.
(1050.degree. F.).
[0003] Hydrocracking is generally accomplished by contacting in a
hydrocracking reaction vessel or zone the gas oil or other
feedstock to be treated with a suitable hydrocracking catalyst
under conditions of elevated temperature and pressure in the
presence of hydrogen so as to yield a product containing a
distribution of hydrocarbon products desired by the refiner.
Generally, middle distillates are the most desirable products,
naphtha and gasoline are less desirable, and light ends comprising
hydrocarbons with 1 to 4 carbons are the least desirable. The
operating conditions and the hydrocracking catalyst within the
hydrocracking reactor influence the yield of the hydrocracked
products.
[0004] Traditionally, the fresh feedstock for a hydrocracking
process is first introduced into a denitrification and
desulfurization reaction zone particularly suited for the removal
of sulfur and nitrogen contaminants. Subsequently, the feedstock is
introduced into a hydrocracking zone containing hydrocracking
catalyst. Within the hydrocracking zone, heavier components of the
hydrocarbon feedstock tend to undergo cracking before lighter
components of the hydrocarbon feedstock. Specifically, cracking
catalysts show at least some selectivity toward cracking heavier
components, i.e., components having higher boiling temperatures,
over lighter components, i.e., components having lower boiling
temperatures. Thermodynamically, cracking of heavier hydrocarbon
components is preferred as such cracking results in a larger
increase in entropy. Conventional processes tend to have poor
selectivity toward middle distillates.
[0005] Accordingly, it is desirable to provide methods and
apparatuses for upgrading hydrocarbon streams with improved
efficiency. In addition, it is desirable to provide methods and
apparatuses that economically hydrocrack hydrocarbon streams.
Furthermore, other desirable features and characteristics will
become apparent from the subsequent detailed description and the
appended claims, taken in conjunction with the accompanying
drawings and the foregoing technical field and background.
BRIEF SUMMARY
[0006] Methods and apparatuses for hydrocracking hydrocarbons are
provided. In an exemplary embodiment, a method for processing a
hydrocarbon stream including lighter hydrocarbons and heavier
hydrocarbons includes hydrocracking the lighter hydrocarbons in a
hydrocracking reactor. After hydrocracking the lighter
hydrocarbons, the method hydrocracks the heavier hydrocarbons in
the hydrocracking reactor. The method includes removing from the
hydrocracking reactor a hydrocracking effluent comprising a mixture
of components formed by hydrocracking the lighter hydrocarbons and
hydrocracking the heavier hydrocarbons.
[0007] In another embodiment, a method for processing hydrocarbons
includes fractionating the hydrocarbons into a stream rich in
lighter hydrocarbons and a stream rich in heavier hydrocarbons. The
method includes feeding the stream rich in lighter hydrocarbons to
an upstream location in a hydrocracking zone and hydrocracking the
stream rich in lighter hydrocarbons to form lighter hydrocracking
products. Further, the method includes feeding the stream rich in
heavier hydrocarbons into the lighter hydrocracking products at a
downstream location in the hydrocracking zone and hydrocracking the
stream rich in heavier hydrocarbons to form heavier hydrocracking
products.
[0008] In accordance with another exemplary embodiment, an
apparatus for processing a hydrocarbon stream is provided. The
apparatus includes a fractionation unit having an upper outlet and
a lower outlet and configured to discharge a stream rich in lighter
hydrocarbons from the upper outlet and a stream rich in heavier
hydrocarbons from the lower outlet. The apparatus further includes
a hydrocracking reactor having an upper inlet in fluid
communication with the upper outlet of the fractionation unit for
receiving the stream rich in lighter hydrocarbons. The
hydrocracking reactor includes an upper hydrocracking zone for
hydrocracking the stream rich in lighter hydrocarbons. Also, the
hydrocracking reactor includes a lower inlet in fluid communication
with the lower outlet of the fractionation unit for receiving the
stream rich in heavier hydrocarbons. Further, the hydrocracking
reactor includes a lower hydrocracking zone for hydrocracking the
stream rich in heavier hydrocarbons.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Embodiments of methods and apparatuses for hydrocracking
hydrocarbons will hereinafter be described in conjunction with the
following drawing figure wherein:
[0010] FIG. 1 is a schematic diagram of an apparatus for
hydrocracking hydrocarbons in accordance with an embodiment.
DETAILED DESCRIPTION
[0011] The following detailed description is merely exemplary in
nature and is not intended to limit the methods and apparatuses for
hydrocracking hydrocarbons claimed herein. Furthermore, there is no
intention to be bound by any theory presented in the preceding
background or the following detailed description.
[0012] As described herein, methods and apparatuses provide
increased efficiency for hydrocracking conversion of hydrocarbon
streams by hydrocracking lighter components before hydrocracking
heavier components. As used herein, "heavy" and "light" components
refer to the relative boiling temperature of components. Thus, a
"heavy" component has a higher boiling temperature than a "light"
component. Accordingly, a "heaviest" component has a higher boiling
temperature than a "heavier" component that, in turn, has a higher
boiling temperature than a "lighter" component. The hydrocracking
process may be a once-through process, i.e., using a single pass of
a hydrocarbon stream through a hydrocracking zone. The exemplary
methods and apparatuses described herein fractionate the
hydrocarbon feed stream into a heavy and light fraction (or into
more than two fractions such as heaviest, heavier, and lighter
fractions). Each fraction is fed to the hydrocracking zone, with
the lightest fraction fed to the most upstream catalyst bed, the
heaviest fraction fed to the most downstream catalyst bed, and
middle fractions fed to respective middle catalyst beds. As a
result, hydrocracking reactions are performed on lighter fractions
before heavier fractions. In this manner, the methods and
apparatuses prevent the concentration of unconverted lighter
components of the hydrocarbon feedstock from decreasing in
proportion to the concentration of cracked products of the heavier
components of the hydrocarbon feedstock. Thus, catalyst selectivity
is not decreased at high conversion conditions.
[0013] The methods and apparatuses described herein differ from
conventional processing, in which a hydrocarbon stream including
heavy and light components is fed into a hydrocracking zone.
Conventionally, the heavier components are selectively hydrocracked
over lighter components. As the heavier components are cracked, the
concentration of unconverted lighter components of the hydrocarbon
feedstock decreases in proportion to the concentration of cracked
products of the heavier components of the hydrocarbon feedstock. As
that concentration decreases, the catalyst in the hydrocracking
zone becomes more likely to convert, or re-crack, cracked products
rather than cracking unconverted lighter components. This results
in a decrease in selectivity to middle distillates when operating
at high conversion rate conditions with a simultaneous decrease in
incremental conversion, i.e., increased conversion of unconverted
components per degree of increased temperature or per unit of
increased catalyst volume.
[0014] As described herein, the exemplary methods and apparatuses
efficiently process hydrocarbon streams by hydrocracking lighter
hydrocarbon components separately from heavier hydrocarbon
components. In this manner, selectivity to middle distillates in
increased over conventional processing. In an exemplary embodiment,
a hydrocarbon feed stream is fractionated into at least two
streams, such as a stream rich in heavy components having boiling
temperatures in a first temperature range and a stream rich in
light components having boiling temperatures in a second
temperature range less than the first temperature range. As
referred to herein, "rich in" the component referred to means that
the referenced stream has a higher content of the subject component
than any other stream that is produced through fractionation and/or
subject to hydrocracking. In embodiments, the streams that are
"rich in" the subject component have a content of the component of
at least 50 weight % (wt %), based on the total weight of the
subject component. In exemplary embodiments, a stream "rich in" a
subject component has a content of the component of at least 75 wt
%, such as at least 90 wt %. In certain embodiments, a stream "rich
in" a subject component has a content of the component of at least
95 wt % or at least 98 wt %. The stream rich in light components is
fed to a hydrocracking zone at an upstream location and undergoes
hydrocracking to form hydrocracking products. Then, the stream rich
in heavy hydrocarbon components is added to the hydrocracking zone
at a downstream location. With the reduced presence of heavier
components and the hydrocracked products of heavy components in the
upstream portion of the hydrocracking zone, the light components
are more efficiently hydrocracked. Further, the introduction of the
stream rich in heavy components at the downstream location serves
to quench the hydrocracking products from the light hydrocarbon
components. As a result, inter-bed hydrogen quenching may be
unnecessary in the exemplary methods and apparatuses.
[0015] FIG. 1 is a schematic of an apparatus 10 for processing a
hydrocarbon feed stream 15 in accordance with an exemplary
embodiment. An exemplary hydrocarbon feed stream 15 may be formed
as a bottom stream from a vacuum fractionation zone (not shown). As
used herein, "bottom stream" refers to a stream withdrawn at or
near a bottom of a column, such as a distillation column The
exemplary feed stream may also include heavy hydrocarbons, such as
light cycle oil and vacuum gas oil. As used herein, "light cycle
oil" refers to a hydrocarbon material boiling in a range of from
about 204.degree. C. to about 343.degree. C. (about 400.degree. F.
to about 650.degree. F.) and can include one or more
C.sub.13-C.sub.18 hydrocarbons, and "vacuum gas oil" refers to a
hydrocarbon material boiling in the range of from about 343.degree.
C. to about 524.degree. C. (about 650.degree. F. to about
975.degree. F.) and can include one or more C.sub.22-C.sub.45
hydrocarbons. Exemplary hydrocarbon feed streams 15 suitable for
processing by the apparatus 10 are vacuum gas oils having boiling
points in the range of about 370.degree. C. to about 590.degree. C.
(about 700.degree. F. to about 1100.degree. F.), for example from
about 343.degree. C. to about 565.degree. C. (about 650.degree. F.
to about 1050.degree. F.). In addition to, or other than, vacuum
gas oil, particular fresh feed components may include a wide
variety of straight run and converted hydrocarbon fractions
obtained in refinery operations (i.e., derived from crude oil),
such as atmospheric gas oils, vacuum and deasphalted vacuum resids
(e.g., boiling above 565.degree. C. (1050.degree. F.)), atmospheric
resids (e.g., boiling above about 343.degree. C. (650.degree. F.)),
coker distillates, straight run distillates, whole or topped
petroleum crude oils including heavy crude oils, pyrolysis-derived
oils, high boiling synthetic oils, cycle oils and catalytic cracker
(e.g., fluid catalytic cracking or FCC) distillates. Fresh feed
components of the heavy hydrocarbon feed stream 15 may also include
mineral oils and synthetic oils (e.g., tars, bitumen, coal oils,
shale oil, tar sand products, etc.) and fractions thereof.
[0016] As shown, the hydrocarbon feed stream 15 is fed to a
fractionation unit 20. The fractionation unit 20 separates the
hydrocarbon feed stream 15 into light fraction 22 rich in
hydrocarbon components having boiling points in a first range, a
middle fraction 24 rich in hydrocarbon components having boiling
points in a second range higher than the first range, and a heavy
fraction 26 rich in hydrocarbon components having boiling points in
a third range higher than the second range. For example, the light
fraction may be rich in hydrocarbons having boiling points of less
than about 425.degree. C. (less than about 800.degree. F.), the
middle fraction may be rich in hydrocarbons having boiling points
of from about 425.degree. C. to about 480.degree. C. (about
800.degree. F. to about 900.degree. F.), and the heavy fraction may
be rich in hydrocarbons having boiling points of greater than about
480.degree. C. (900.degree. F.).
[0017] While FIG. 1 illustrates fractionation of the hydrocarbon
feed stream into three fractions, it is contemplated that in other
embodiments, the hydrocarbon feed stream 15 can be fractionated
into two fractions, or four or more fractions. For example, the
fractionation unit 20 may fractionate the hydrocarbon feed stream
15 into two fractions including a light fraction 22 rich in
hydrocarbons having boiling points of from about 370.degree. C. to
about 450.degree. C. (about 700.degree. F. to about 850.degree. F.)
and into a heavy fraction 26 rich in hydrocarbons having boiling
points of from about 450.degree. C. to about 590.degree. C. (about
850.degree. F. to about 1100.degree. F.).
[0018] As shown in FIG. 1, each fraction 22, 24 and 26 is fed to a
hydrocracking zone 30. As used herein, the term "zone" can refer to
an area including one or more equipment items and/or one or more
sub-zones. Equipment items can include one or more reactors or
reactor vessels, heaters, exchangers, pipes, pumps, compressors,
and controllers. Additionally, an equipment item, such as a
reactor, dryer, or vessel, can further include one or more zones or
sub-zones. In an exemplary embodiment, the hydrocracking zone 30
encompasses a single hydrocracking reactor. As shown, the
hydrocracking zone 30 includes catalyst beds 32, 34, and 36
arranged in series. Also, the hydrocracking zone 30 receives a
hydrogen stream 38. The hydrogen stream 38 may be introduced
through the fraction 22 or directly into the hydrocracking zone 30
as shown.
[0019] The light fraction 22 is introduced to the hydrocracking
zone 30 at a location 42 above and upstream of the catalyst bed 32.
As a result, it undergoes hydrocracking over the catalyst bed 32 in
the hydrogen atmosphere of the hydrocracking zone 30 and forms
hydrocracking products 52 that move in a downward direction through
the catalyst bed 32. In an exemplary embodiment, at least about 50
weight percent (wt %) of the light fraction 22 is converted to
hydrocracking products 52, such as at least about 60 wt % of the
light fraction 22, or for example, at least about 70 wt % of the
light fraction 22. The hydrocracking products 52 are lighter than
the light fraction 22 and typically have boiling points of from
about 150.degree. C. to about 370.degree. C. (about 300.degree. F.
to about 700.degree. F.).
[0020] As shown, the middle fraction 24 is introduced to the
hydrocracking zone 30 at a location 44 below and downstream of the
catalyst bed 32 and above and upstream of the catalyst bed 34. The
middle fraction 24 enters the hydrocracking zone 30 and is fed into
the hydrocracking products 52 formed at the catalyst bed 32. The
middle fraction 24 undergoes hydrocracking over the catalyst bed 34
in the hydrogen atmosphere and forms hydrocracking products 54
that, with the hydrocracking products 52, move in a downward
direction through the catalyst bed 34. The catalyst bed 34 is
selective toward the heavier components of the middle fraction 24
over the hydrocracking products 52 from the catalyst bed 32, as the
heavier components of the middle fraction 24 are significantly
heavier than the hydrocracking products 52. In an exemplary
embodiment, at least about 90 wt % of the middle fraction 24 is
converted to hydrocracking products 54, such as at least about 95
wt % of the middle fraction 24, or for example, at least about 99
wt % of the middle fraction 24. The hydrocracking products 54 are
lighter than the middle fraction 24 and typically have boiling
points of from about 150.degree. C. to about 370.degree. C. (about
300.degree. F. to about 700.degree. F.).
[0021] As shown, the heavy fraction 26 is introduced to the
hydrocracking zone 30 at a location 46 below and downstream of the
catalyst bed 34 and above and upstream of the catalyst bed 36. The
heavy fraction 26 enters the hydrocracking zone 30 and is combined
with the hydrocracking products 52 and 54 formed at the catalyst
beds 32 and 34. The heavy fraction 26 undergoes hydrocracking over
the catalyst bed 36 in the hydrogen atmosphere and forms
hydrocracking products 56 that, with the hydrocracking products 52
and 54, move in a downward direction through the catalyst bed 36.
The catalyst bed 36 is selective toward the heavier components of
the heavy fraction 26 over the hydrocracking products from the
catalyst beds 32 and 34, as the heavier components of the heavy
fraction 26 are significantly heavier than the hydrocracking
products 52 and 54. In an exemplary embodiment, at least about 50
wt % of the heavy fraction 26 is converted to hydrocracking
products, such as at least about 60 wt % of the heavy fraction 26,
or for example, at least about 70 wt % of the heavy fraction 26.
The hydrocracking products 56 are lighter than the heavy fraction
26 and typically have boiling points of from about 150.degree. C.
to about 370.degree. C. (about 300.degree. F. to about 700.degree.
F.).
[0022] In an exemplary embodiment, the hydrocracking reaction
conditions in the hydrocracking zone 30 include a temperature from
about 205.degree. C. to about 480.degree. C. (about 400.degree. F.
to about 900.degree. F.) and a pressure from about 3.5 megapascals
(MPa) to about 20.8 MPa (500 pounds per square inch gauge (psig) to
about 3000 psig). In addition, hydrocracking conditions may include
a liquid hourly space velocity from about 0.1 to about 30
hr.sup.-1.
[0023] Any conventional hydrocracking catalyst may be used in the
hydrocracking catalyst beds 32, 34 and 36. Examples of suitable
catalysts for use in the hydrocracking catalyst beds 32, 34 and 36
include, but are not limited to, those comprising a metal selected
from the group consisting of iron, nickel, cobalt, tungsten,
molybdenum, vanadium, ruthenium, and mixtures thereof, deposited on
a support containing a zeolite or another component exhibiting
Bronsted acidity. Representative zeolites for hydrocracking
catalyst supports include beta zeolite, Y zeolite and MFI
zeolite.
[0024] An exemplary hydrocracking catalyst has a size and shape
that is similar to those of conventional commercial catalysts. An
exemplary hydrocracking catalyst is manufactured in the form of a
cylindrical extrudate having a diameter of from about 0.8
millimeters (mm) to about 3.2 mm ( 1/32 inches to about 1/8
inches). The catalyst can however be made in any other desired form
such as a sphere or pellet. The extrudate may be in forms other
than a cylinder such as the form of a trilobe or other shape that
has advantages in terms or reduced diffusional distance or pressure
drop.
[0025] An exemplary hydrocracking catalyst may contain a number of
non-zeolitic materials that can beneficially affect particle
strength, cost, porosity, and performance. The other catalyst
components, therefore, make positive contributions to the overall
catalyst even if not necessary as active cracking components. These
other components are part of the catalyst support. Some traditional
components of the support such as silica-alumina normally make some
contribution to the cracking capability of the catalyst. Other
inorganic refractory materials that may be used as a support in
addition to silica-alumina and alumina include for example silica,
zirconia, titania, boria, and zirconia-alumina. These
aforementioned support materials may be used alone or in any
combination.
[0026] An exemplary hydrocracking catalyst may contain a metallic
hydrogenation component. The hydrogenation component may be
provided as one or more base metals uniformly distributed in the
catalyst particle. Noble metals such as platinum and palladium
could be applied or a combination of two base metals may be used.
Specifically, either nickel or cobalt may be paired with tungsten
or molybdenum, respectively.
[0027] An exemplary hydrocracking catalyst can be formulated using
industry standard techniques. This can be summarized as admixing a
zeolite with the other inorganic oxide components and a liquid such
as water or a mild acid to form an extrudable dough followed by
extrusion through a multihole die plate. The extrudate is collected
and may be calcined at high temperature to harden the extrudate.
The extruded particles are then screened for size and the
hydrogenation components are added as by dip impregnation or the
well known incipient wetness technique. If the catalyst contains
two metals in the hydrogenation component these may be added
sequentially or simultaneously. The catalyst particles may be
calcined between metal addition steps and again after the metals
are added. The finished catalyst may have a surface area between
about 200 and 600 m.sup.2/g and an average bulk density (ABD) from
about 0.8 to about 1.0 g/cc.
[0028] As shown, the hydrocracking products 52, 54 and 56 exit the
hydrocracking zone 30 as an effluent stream 60 from outlet 62.
Further processing of the effluent stream 60 may include
fractionation, denitrification, desulfurization, stripping and
washing to form product streams such as naphtha, kerosene, and/or
diesel streams and to recover vacuum gas oil.
[0029] Any of the above components of the hydrocarbon feed stream
15 may be hydrotreated prior to being introduced into the
hydrocracking zone 30, to remove, for example, sulfur and/or
nitrogen compounds such that the fractions 22, 24 and 26 will have
total sulfur and nitrogen levels below, for example, 500 ppm by
weight and 100 ppm by weight, respectively. Hydrotreating may be
performed in a separate hydrotreating reactor or in the same
reactor as used for hydrocracking by incorporating, for example, a
bed of hydrotreating catalyst upstream of each bed of hydrocracking
catalyst. If hydrotreating is performed in a separate hydrotreating
reactor, there may be additional zones upstream of zone 20 in which
various separation operations are performed, including but not
limited to vapor-liquid disengaging, steam stripping, flash
separation by reduction of pressure, and/or distillation. The
lower-boiling material removed in these operations would not be fed
into zone 20.
[0030] The exemplary hydrocracking zone 30 includes a total
catalyst volume. Accordingly, each catalyst bed in the
hydrocracking zone 30 includes a fraction of the total catalyst
volume. Further, the hydrocarbon feed stream 15 has a total
hydrocarbon volume and each fraction 22, 24 and 26 of hydrocarbons
includes a feed volume fraction of the total hydrocarbon volume. In
an exemplary embodiment, the fraction of the total catalyst volume
in the upper bed 32 does not exceed the feed volume fraction of the
fraction 22 fed to the upper bed 32. Likewise, the fraction of the
total catalyst volume in any second, non-bottom bed 34 does not
exceed the feed volume fraction of the fraction 24 fed to the
second, non-bottom bed 34. However, the fraction of the total
catalyst volume in the bottom bed 36 does exceed the feed volume
fraction of the fraction 26 fed to the bottom bed 36. For example,
in a hydrocracking zone 30 having two beds 32 and 36, the fraction
22 may be formed from two-thirds of the hydrocarbon feed stream 15
and the fraction 26 may be formed from one-third of the hydrocarbon
feed stream 15. In such an embodiment, no more than two-thirds of
the total catalyst volume in the hydrocracking zone 30 will be in
the upper catalyst bed 32 and at least one-third of the total
catalyst volume in the hydrocracking zone 30 will be in the lower
catalyst bed 36.
[0031] The methods and apparatuses described herein provide
increased efficiency for hydrocracking conversion of hydrocarbon
streams and may be implemented in a once-through process, i.e., in
embodiments, the hydrocarbon streams pass only once through the
hydrocracking zone. The methods and apparatuses fractionate the
hydrocarbon feed stream into a heavy and light fraction (or into
more than two fractions such as heaviest, heavier, and lighter
fractions). Each fraction is fed to the hydrocracking zone, with
the lightest fraction fed to the most upstream catalyst bed, the
heaviest fraction fed to the most downstream catalyst bed, and
middle fractions fed to respective middle catalyst beds. As a
result, hydrocracking reactions are performed on lighter fractions
before heavier fractions. In this manner, the methods and
apparatuses prevent the concentration of unconverted lighter
components of the hydrocarbon feedstock from decreasing in
proportion to the concentration of cracked products of the heavier
components of the hydrocarbon feedstock. Thus, catalyst selectivity
to middle distillates is not decreased at high conversion
conditions.
[0032] Further, the addition of heavier fractions at inter-bed
locations provides for quenching of the hydrocracking products
formed at upstream catalyst beds. As a result, hydrogen need not be
added at inter-bed location as in conventional apparatuses.
[0033] While at least one exemplary embodiment has been presented
in the foregoing detailed description, it should be appreciated
that a vast number of variations exist. It should also be
appreciated that the exemplary embodiment or exemplary embodiments
are only examples, and are not intended to limit the scope,
applicability, or configuration of the claimed subject matter in
any way. Rather, the foregoing detailed description will provide
those skilled in the art with a convenient road map for
implementing an exemplary embodiment or embodiments. It being
understood that various changes may be made in the function and
arrangement of elements described in an exemplary embodiment
without departing from the scope set forth in the appended
claims.
* * * * *